The use of linear feedback shift registers (LFSRs) is well known in integrated circuit technology. LFSRs may be used in a number of applications. For example, a LFSR may be used to implement a clock divider circuit. A clock divider circuit is used to divide a master clock signal to obtain a different frequency clock signal. A LFSR (n bit width) may also be used as both a test data generation circuit and a test result generation circuit. A LFSR serving as a test data generation circuit typically includes a simple register circuit including serial-connected n D-type flip-flops and a feedback circuit for generating an exclusive-OR (XOR) signal of outputs of predetermined flip-flops and supplying the signal to an input terminal of a first one of the serially-connected flip-flops.
LFSR circuits as described above are further implemented for data encryption. More specifically, data encryption techniques are used to increase the security in data exchange and transfer over a shared transmission channel. In its simplest form, data encryption uses a “key” based on a particular algorithm to change the sequence of a package of data that contains a piece of confidential information (“plaintext”) so that the data is enciphered or “scrambled” into an form that appears to have no correlation with the embedded confidential information (“ciphertext”). An unauthorized user, who does not have the knowledge of either the encryption method (e.g., the encryption algorithm) or the key formed based on the encryption method, cannot easily in the scrambled data by using a “key” that is constructed based on the encryption method. Therefore, even if the unauthorized user obtains the scrambled data, the knowledge of both of the encryption method and the particular key is needed to decrypt the confidential information embedded therein.
One well-known encryption technique using LFSRs is the generation of maximal length pseudo random bit sequences (PRBS). Currently, however, PRBS generation and other similar known encryption systems and techniques are at most capable of encryption and decryption at rates of substantially 1 GBit/sec. Furthermore, current PRBS generating systems implementing LFSRs have large form factors and include relatively expensive components. However, as information exchange and transfer rates of communication systems increase, so does the need for encryption systems that are capable of encryption at compatible rates. In addition, with available component space in communication systems decreasing, there is also a need for encryption systems of smaller sizes and of decreased cost.